Re: [PATCH 14/16] virtio-net: support queue_enable for vhost-user

[Kangjie Xu <kangjie.xu@linux.alibaba.com>]

在 2022/7/26 12:25, Jason Wang 写道:
>
> 在 2022/7/18 19:17, Kangjie Xu 写道:
>> Support queue enable in vhost-user scenario. It will be called when
>> a vq reset operation is performed and the vq will be restared.
>>
>> It should be noted that we can restart the vq when the vhost has
>> already started. When launching a new vhost-user device, the vhost
>> is not started and all vqs are not initalized until
>> VIRTIO_PCI_COMMON_STATUS is written. Thus, we should use vhost_started
>> to differentiate the two cases: vq reset and device start.
>>
>> Signed-off-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> ---
>>   hw/net/virtio-net.c | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 8396e21a67..2c26e2ef73 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -544,6 +544,25 @@ static void virtio_net_queue_reset(VirtIODevice 
>> *vdev, uint32_t queue_index)
>>       assert(!virtio_net_get_subqueue(nc)->async_tx.elem);
>>   }
>>   +static void virtio_net_queue_enable(VirtIODevice *vdev, uint32_t 
>> queue_index)
>> +{
>> +    VirtIONet *n = VIRTIO_NET(vdev);
>> +    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(queue_index));
>> +    int r;
>> +
>> +    if (!nc->peer || !vdev->vhost_started) {
>> +        return;
>> +    }
>> +
>> +    if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_USER) {
>> +        r = vhost_virtqueue_restart(vdev, nc, queue_index);
>> +        if (r < 0) {
>> +            error_report("unable to restart vhost net virtqueue: %d, "
>> +                            "when resetting the queue", queue_index);
>> +        }
>> +    }
>> +}
>
>
> So we don't check queue_enable in vhost_dev_start(), does this mean 
> the queue_enable is actually meaningless (since the virtqueue is 
> already started there)?
>
> And another issue is
>
> peet_attach/peer_detach() "abuse" vhost_set_vring_enable(). This 
> probably means we need to invent new type of request instead of 
> re-using VHOST_USER_SET_VRING_ENABLE.
>
> Thanks
>
>
1. Yes, we don't need queue_enable in vhost_dev_start(), queue_enable is 
only useful when restarting the queue. I name it as queue_enable() 
simply because it is called when VIRTIO_PCI_COMMON_Q_ENABLE is written. 
Would it look better if we rename it as "queue_reenable"?

2. I think inventing a new type of vhost-protocol message can be a good 
choice. However, I don't know much about the vhost protocol. If we want 
to add a new message in vhost protocol, except the documentation and the 
code in qemu, Do we need to submit patches to other projects, e.g. some 
projects like virtio-spec?

Thanks

>> +
>>   static void virtio_net_reset(VirtIODevice *vdev)
>>   {
>>       VirtIONet *n = VIRTIO_NET(vdev);
>> @@ -3781,6 +3800,7 @@ static void virtio_net_class_init(ObjectClass 
>> *klass, void *data)
>>       vdc->bad_features = virtio_net_bad_features;
>>       vdc->reset = virtio_net_reset;
>>       vdc->queue_reset = virtio_net_queue_reset;
>> +    vdc->queue_enable = virtio_net_queue_enable;
>>       vdc->set_status = virtio_net_set_status;
>>       vdc->guest_notifier_mask = virtio_net_guest_notifier_mask;
>>       vdc->guest_notifier_pending = virtio_net_guest_notifier_pending;